And because AC is equally divided
According to the triangle principle, if two angles are equal, then two conditional edges are equal.
Then BC=AB
Similarly:. AD=AB。
So: AB=AD=BC
Because AE//BF, and then AD//BC.
According to the diamond judgment rule: three sides of a quadrilateral are equal and two adjacent sides are parallel.
It can be confirmed that ABCD is a diamond.
The second train of thought:
Because AE//BF, then
And because AC is equally divided
According to the triangle principle, if two angles are equal, then two conditional edges are equal.
Then BC=AB
The same goes for the front.
Because BD is divided equally
So < ADB = & ltDBC< associate doctor.
Another reason
So < AOB = & ltAOD=90 degrees.
Namely: AC vertical BD (it has been proved above that BC=AB)
According to the diamond judgment rule: two diagonal lines of a quadrilateral are vertical and two adjacent sides are equal, it can be proved that this quadrilateral is a diamond.